Syria accused the opposition of pushing for foreign intervention and trying to sabotage an Arab-brokered deal for observers, but ignoring calls for talks.

Reacting to reports of hundreds of civilians being killed this week, the SNC called for an "emergency UN Security Council session to discuss the regime’s massacres in Zawiyah mountain, Idlib, and Homs, in particular."

It also appealed for an "emergency meeting for the Arab League to condemn the bloody massacres ... and cooperate with the United Nations in taking the necessary measures to protect Syrian civilians."

The United States warned of new international measures to pressure Syria to halt its bloody crackdown, and said Assad did "not deserve to rule."

The White House said that if Damascus did not fully implement an Arab League plan to contain the violence, "the international community will take additional steps to pressure the Assad regime to stop its crackdown."

The SNC, a major umbrella group of factions opposed to Assad, reported "250 fallen heroes during a 48-hour period." It urged the Security Council to declare the cities and towns under attack "'safe zones' that enjoy international protection; and force the regime's forces to withdraw from said areas."

A witness and two activist groups said Wednesday that government forces surrounded residents of a restive village in a valley and killed all those trapped inside — more than 100 people — in a barrage of rockets, tank shells, bombs and gunfire that lasted for hours.

The attack on Tuesday pushed the death toll for two days of violence across Syria to more than 200, and was one of the deadliest single events of the entire nine-month uprising against Assad's rule.

The offensive targeted the village of Kfar Owaid, about 50 km from the northern border with Turkey. It is part of the rugged mountainous region of Jabal Al-Zawiyah, which has been the scene of clashes between troops and army defectors and intense anti-government protests for weeks.